Electrical component handlers receive electrical circuit components, e.g., ceramic capacitors, present the electrical circuit components to an electronic tester for testing, and sort the electrical circuit components according to the results of the testing. An exemplary electrical component handler is described in U.S. Pat. No. 5,842,579 to Garcia et al. (the '579 patent), which is assigned to Electro Scientific Industries, Inc., the assignee of the present patent application. Design and operational advantages of the electrical component handler of the '579 patent include 1) the elimination of manual seating of components for test purposes and manual sorting; 2) the ability to handle a greater quantity of components per unit time than prior art electrical component handlers are able to handle; 3) the ability to take a randomly oriented heap of components and properly orient them; 4) the ability to present the components to a tester in multiples; and 5) the ability to sort the tested parts into a plurality of receiving or sorting bins.
FIG. 1 is a pictorial drawing of an electrical component handler 2 as described in the '579 patent. In the electrical component handler 2, one or more concentric rings 3 of component seats 4 formed in an annular test plate 5 are rotated in a clockwise direction around a turntable hub 6. As the test plate 5 turns, the component seats 4 pass beneath a loading area 10, a contact head 11 of five contact modules 12 (two shown in FIG. 1), and an ejection manifold 13. In the loading area 10, electrical circuit components or devices-under-test (DUTs) 14 (FIG. 3) are poured into the concentric rings 3, causing unseated DUTs 14 to tumble randomly until they are seated in the test plate seats 4. The DUTs 14 are then rotated beneath the contact head 11, and each DUT 14 is electrically contacted and parametrically tested. Once the DUTs 14 have been tested, the ejection manifold 13 ejects the DUTs 14 from their seats by blasts of air from selectively actuated, spatially aligned pneumatic valves. Ejected DUTs 14 are preferably directed through ejection tubes 15a into sorting bins 15b. 
FIGS. 2 and 3 show the prior art contact head 11 of the '579 patent in greater detail. Specifically, FIG. 2 shows a pictorial drawing of the contact head 11 with less than a full complement of the contact modules 12 mounted thereon; and FIG. 3 is a fragmentary sectional view taken along lines 3-3 of FIG. 2 juxtaposed with a fragmentary cross-sectional view of a DUT 14 seated in the test plate 5. With reference to FIGS. 2 and 3, contact module 12 includes a plurality of upper contacts 16 and lower contacts 18 (one each shown in FIG. 3) for coupling the DUT 14 to the test plate 5. The upper contacts 16 are resilient flat metal cantilevered leaves with inclined elongated tips that project away at a shallow angle from the test plate 5. The upper contacts 16 flex slightly when they encounter the seated DUTs 14 to provide a downward contact force that is largely dictated by the thicknesses and/or end widths of the leaves. The elongated tips prevent the seated DUTs 14 from popping out of their seats (as a consequence of a “tiddlywink” effect) as the leaves pass over the back edges of the DUTs 14 as the test plate 5 advances forward. The tips of the upper contacts 16 may be coated with a metal alloy to minimize contact resistance.
The lower contacts 18 are typically stationary contacts in the form of cylinders. As shown in FIG. 4, an exemplary prior art lower contact 18 is an elongated cylinder having upper and lower planar surfaces, a central conductive core 22, and an electrically insulating outer sleeve 24. The lower contact 18 extends through holes 30 formed in a vacuum plate 32 and set between adjacent vacuum channels 34 such that the lower contact 18 is in alignment with its corresponding upper contact 16 and its corresponding component seat ring 3. The vacuum channels 34 may be aligned with vacuum ports 13 (FIG. 5) in the test plate 5 that are connected to each component seat 4 by a vacuum network (not shown) in the test plate 5. The vacuum pressure may be used to help hold the electrical components 14 within the component seats 4.
A base member 36 positioned below the vacuum plate 32 includes an upwardly projecting wall 38 formed of contiguous cylindrical scallop segments 40 that receive a row of the cylinders of the lower contacts 18. A releasable clamping mechanism 42 pushes and thereby pins the outer sleeves 24 of the lower contacts 18 against their associated scallop segments 40 of the wall 38 to maintain their orientation normal to the test plate 5. Thus, for each row of the lower contacts 18, there is a clamping mechanism and a pinning wall. A corresponding plurality of spring-biased pin contacts 44 (e.g., “pogo” pins) extends through a plurality of slots (not shown) in the bottom of the base member 36 to make electrical contact with the central cores 22 of the lower contacts 18. There is one base slot for each row of the lower contacts 18. The pin contacts 44 are preferably mounted lengthwise by their spring-biased ends in holders 46, four for each holder 46 to match a row of the lower contacts 18. Each holder 46 is affixed in a different base slot. The pin contacts 44 are coupled to the tester electronics through wires 48.
The contact head 11 includes five contact modules 12. This embodiment includes 20 upper contacts 16, five for each ring 3 of component seats 4. Each of 20 lower contacts 18 is positioned on the opposite side of the test plate 5 and in alignment with a different one of the 20 upper contacts 16, as indicated in FIG. 3 for one pair of the upper and lower contacts 16 and 18. Thus, the contact head 11 includes a full complement of contact modules 12 in which the terminals of 20 DUTs 14 can be contacted simultaneously, thereby simultaneously coupling all 20 of them to the test plate 5.
The upper and lower contacts 16 and 18 of the contact modules 12 become contaminated during operation of the electrical component handler 2. Exemplary contamination sources include friction polymerization; external debris, such as material deposits from previously tested devices; and naturally occurring oxide formation on the contact surface. Additionally, some amount of debris, such as broken devices, plating media, or fragments of refractory carriers, is typically present in or on the DUTs 14. This debris is often introduced into the test system and subsequently placed in contact with the lower contacts 18. Contamination of the upper and lower contacts 16 and 18 creates contact resistance variation that is additive to the actual resistance measurement for each DUT 14. This contamination of upper and lower contacts 16 and 18 results in rejection of acceptable DUTs 14, resulting in yield loss and a reduction in the mean time between assists (MTBA) associated with the electrical component handler 2. When such conventional handling and testing methods are used, up to 10% of the DUTs 14 are falsely rejected. These falsely rejected components are then either re-tested or thrown away as scrap. Both instances cause extra processing time and cost.
FIG. 5A is a simplified fragmentary cross-sectional view of a test plate 5 and vacuum plate 32 taken along a radial line extending medially through a row of component seats, and FIG. 5B is a simplified fragmentary cross-sectional view of a test plate and vacuum plate taken along a radial line extending medially through a row of component seats and the lower contacts. With reference to FIGS. 3-5, a bottom surface 50 of the test plate 5 is currently employed to wipe the top end 52 of the cores 22 of the lower contacts 18 clean. Unfortunately, the top ends 52 of the lower contacts 18 become contaminated eventually, despite the cleaning action of the test plate 5.
Consequently, periodic cleaning of the upper and lower contacts 16 and 18 may be required to facilitate accurate DUT measurement. The most common prior art method of cleaning the upper and lower contacts 16 and 18 entails stopping operation of the electrical component handler 2 and mechanically cleaning the upper and lower contacts 16 and 18. However, stopping the electrical component handler 2 results in lost productivity and reduces machine throughput by lowering the MTBA.
Another prior art method of removing contamination and debris entails the use of jam sensors or jam-clearing mechanisms. Implementing these additional devices increases the manufacturing and repair costs, as well as the mechanical complexity, of the electrical component handler 2.
Thus a need exists for an effective and efficient a way to carry out cleaning the contacts 18 of an electrical component handler 2.